Check valves of the kind initially described or similar to it are already on the market in large numbers. In a known check valve of the initially cited kind, the housing is provided with a radial liquid inlet and an axial liquid outlet. The valve ball is forced by a conical compression spring into its valve seat. The valve ball is guided only by the helical compression spring which when the valve is open is compressed into a block by the flow pressure of the liquid passing through the valve. Because the compression spring is forced into a block, free flow through of the liquid through the check valve is hampered, that is, the flow resistance is substantially increased. Furthermore, the valve ball cannot be optimally guided by the compression spring alone.
The known check valve is provided with longitudinal ribs attached to or shaped from the outside surface of its housing, which thereby keep a sleeve-shaped screen slipped onto said housing radially spaced from its outside surface. The sleeve like screen consists of a metal wire and covers the entire housing outside surface, including the radial liquid inlet. Because of the radial liquid inlet and the ensuing deflection of the liquid, a further disadvantageous increase in flow resistance is incurred.
It is the object of the present invention to so design a check valve of the initially discussed type that the flow resistance is reduced to a minimum and that reliable operation of the check valves is ensured by an accurate guidance of the valve ball. Furthermore it is the object of this invention to design the check valve in such a manner that it is simple and economical to assemble and to manufacture.
This problem is essentially solved by the invention in that the valve ball is guided by longitudinal ribs mounted to the inside wall in the inside space of the housing. Appropriately at least three, preferably four guide ribs are arranged mutually uniformly spaced circumferentially.
These guide ribs preferably are made unitary with the housing as plastic injection molded parts and achieve a defect-free guidance of the valve ball, whereby the compression spring need only assume henceforth a purely closing function, while the ball is guided by the ribs instead of the spring.
In a preferred embodiment of the invention, the valve bottom comprises a central guide pin on which is mounted the compression spring, and the free end of the guide pin is used as the back stop for the spring excursion of the valve ball. Thereby block-formation in the spring is advantageously averted, and as a consequence the low flow resistance within the check valve remains preserved.
In order to further reduce the flow resistance, the liquid inlet advantageously admits the liquid from the end side, that is in the axial direction of the check valve. As regards such a check valve with an end or axial liquid inlet, the invention in an advantageous design process that the cylindrical screen comprise a bottom covering the end-side liquid outlet. This essential concept is easily translated into practice if the cylindrical screen together with the end-side screen bottom are made by plastic injection molding methods.